This invention relates to a wheel hub, particularly but not exclusively to a hub for a wheelchair wheel.
Wheelchairs are used by physically handicapped people to give them mobility. They are conventionally propelled by the user who rotates handwheels fixed to the road wheels. The handwheels are centred on the axis of rotation of the road wheels. In most cases, the handwheels are rigidly fixed to the road wheels so that one revolution of the hand wheels equates to one revolution of the road wheels.
When the wheelchair is stationary, a brake should be applied to prevent the wheelchair from moving unintentionally. It is known to use brakes which press against the tyre of the road wheel.
EP-A-0 220 734 describes a wheelchair brake which can be set in three different positions. In one position there is no restraint on the wheel which can rotate freely in either direction. In a second position the wheel can only rotate in one (forwards) direction. In the third position, the wheel is braked and cannot rotate at all.
According to the invention, there is provided a wheel hub which comprises a spindle, a sleeve rotatable relative to the spindle through a bearing, and a manually operable device which has three operating positions, a first of which allows free rotation between the spindle and the sleeve, a second of which locks the spindle to the sleeve to effect a braking action, and a third of which engages a ratchet arrangement which allows the spindle to rotate relative to the sleeve in one direction only, characterised in that the manually operable device is fitted on the hub. Fitting the manually operable device on the hub allows the wheel to be easily attached and reattached to the wheelchair frame without having to dismantle the mechanism which controls the wheel rotation.
The wheel hub is particularly intended for use on the wheels of a wheelchair. A hub will be fitted at the centre of each of the main driving wheels of the chair.
The ratchet arrangement produces a feature referred to as xe2x80x98anti-rollbackxe2x80x99. In other words, this position is engaged by the user when the wheelchair is going uphill and prevents the wheel chair from rolling back down the hill if the user stops turning the handwheels.
The selection of one of the three positions is preferably carried out by manipulating a selector mounted on the hub itself. The selector may be a rotatable disc mounted for rotation about an axis coincident with the hub axis. The selector may have a central position corresponding to the first operating position, with the second and third operating positions being reached by rotating the selector in one direction for the second operating position and in the opposite direction for the third operating position.
The disc can have a radially outwardly extending lever to enable it to be turned, or may have a circumferential surface modified to allow it to be gripped and turned. For example the surface, may be provided with a rubber ring, or may be formed with a type of knurling or similar to increase grip.
The spindle is preferably provided with a mounting bracket by which it can be non-rotatably mounted on the wheelchair frame. This bracket may have axially extending pins or sockets which engage with axially extending sockets or pins on the hub. The hub is preferably provided with a quick detachment mechanism enabling the hub (together with a wheel attached to the hub) to be quickly and easily detached from the wheelchair frame. The spindle may have a radial projection at its inner end which can be retracted to enable the spindle to be inserted in or withdrawn from the mounting bracket. When the projection is extended, relative axial movement between the spindle and the mounting bracket cannot take place, and when the pins and sockets are engaged with one another rotational movement between the spindle and the bracket cannot take place.
The manually operable device preferably comprises a splined annular surface on the spindle surrounded by a body on the sleeve which has a recess in which the splined surface lies so that the body is free to rotate relative to the spindle, and to the splined surface on the spindle, when the hub takes up the first operating position, the device also including a first pin or pins, fixed against rotation relative to the sleeve, which can be moved from a retracted position into the path of relative rotational movement between the body and the splined annular surface to engage with the splines and to thus prevent rotation of the sleeve relative to the spindle (the second operating position) and a second pin or pins, also fixed against rotation relative to the sleeve which can be moved into the path of relative rotational movement between the body and the splined annular surface, when the first pin or pins is in a retracted position, to engage with the splines and to prevent rotation of the sleeve in one rotational direction relative to the spindle but to allow rotation in the opposite rotation direction.
The first pin or pins may have square end profiles which engage between splines on the splined surfaces and the second pin or pins may have end profiles with one square face and one ramp face which engage between splines on the splined surfaces, so that the square face prevents rotation of the sleeve in one rotational direction relative to the spindle and the ramp face allows rotation in the opposite rotation direction. The first pin or pins are preferably diametrically opposite (referred to the spindle axis) to the second pin or pins.
In one embodiment, the body on the sleeve has radially extending passages communicating with the recess and the pins are radially movable pins which can move in and out of the recess to engage, one at a time, with the splined surface. The radially movable pins have lateral lugs which engage in cam tracks inside the selector so that movement of the selector in one rotational direction extends the first pins and movement in the opposite rotational direction extends the second pins.
In another embodiment, the body on the sleeve comprises a radially movable slide plate moving between two fixed parallel slide guides such that the plate can move radially but cannot rotate relative to the guides, the recess being provided in the slide plate and the pine being formed integrally with the plate at opposite regions of the circumference of the recess. Leaf springs mounted internally on the selector bias the opposite ends of the slide plate and, the slide plate ends and the leaf springs are designed so that movement of the selector in each direction causes the leaf springs to ride over a none on the slide plate so that the selector is held in one or other ed position until the selector in manually operated to a different position.
There may be two first pins and two second pins.
The invention also extends to a wheelchair wheel having a hub as set forth above, and to a wheelchair having wheels of this type.